1. Field of the Invention
The invention relates primarily to bicycles, but also to any other human powered vehicles, watercraft, or exercise devices which utilize a foot pedal or handgrip for the operator to convert rotational motion and/or linear motion of his feet or hands, into work, in order to activate the device.
2. Description of Prior Art
Bicycle crank arms in general, provide a means for physically connecting the foot pedals of the bicycle to the crankshaft of the bicycle. In some cases, one of the crank arms is also attached to a chain sprocket, or a set of axially concentric sprockets, which drives a chain for the purpose of transmitting power to the drive wheel of the bicycle. Whether the sprocket is attached directly to the crankshaft or spindle, or indirectly to the spindle through one of the crank arm assemblies, the crank arms enable force exerted on the foot pedals to be transferred into power to propel the bicycle as the foot pedals sweep through each stroke.
Bicycles have evolved from their earliest designs with a pair of bilaterally symmetric and inversely synchronized foot pedals, each connected to the crankshaft or spindle of the vehicle by a generally straight crank arm. As bicycle consumers have come to put more emphasis on light weight and performance, bicycle manufacturers have endeavored to manufacture lighter and better performing bicycles. This quest has led many manufacturers to utilize computer aided design techniques and exotic materials in the creation of their products. Today, the weights of many components on bicycles are usually communicated in gram units, because the emphasis on weight reduction is so great that the units of pounds and ounces are insufficiently explicit for many consumers.
One of the largest concentrations of structural material in a typical bicycle is in the crank arm. That often corresponds to one of the largest concentrations of weight on a bicycle, despite some manufacturers' use of exotic lightweight materials at this location. Reducing weight by using such materials usually leads to a significant cost penalties or other tradeoffs.